Conventionally, various types of pipe joints have been used for connection of pipes, such as refrigerator coolant pipes, through which a fluid flows. Examples of typical pipe joints include a flare joint and a flareless joint (e.g., see Patent Document 1). As shown in FIG. 12(a), the flare joint includes a joint body 101 and a nut 102 screwed onto the joint body 101. A pipe 103 is connected to the joint body 101 such that its flared end portion 103a is disposed between a conical face 101a provided on the joint body 101 and a conical face 102a provided on the nut 102. Then, the nut 102 is screwed onto the joint body 101 to sandwich the end portion 103a between each of the conical faces 101a and 102a, thereby connecting between the pipe 103 and the joint body 101.
On the other hand, as shown in FIG. 13(a), the flareless joint includes a joint body 111, a nut 112 screwed onto the joint body 111, and a sleeve 113 interposed between the joint body 111 and the nut 112. A pipe 114 is connected to the joint body 111 such that its distal end portion 114a is inserted into a joint hole 111a formed on the inner periphery of the joint body 111. Then, the nut 112 is screwed onto the joint body 111 allowing the sleeve 113 to be deformed by a conical guide face 111b provided on the inner periphery of the joint body 111. A front end portion 113a thus bites into an outer periphery 114b of the pipe 114, thereby connecting between the pipe 114 and the joint body.
For example, those refrigerators that include such pipe joints may undergo a pressure-proof test before piping connection or require the prevention of dust particles or moisture intrusion before piping connection, e.g., during transportation. For this reason, the openings of those pipe joints need to be kept sealed. To this end, with no pipe connected to a pipe joint, such a cover structure is configured that allows the opening of the pipe joint to be sealed with a partition cover constructed to be removable from the pipe joint. For example, in a flare joint cover structure shown in FIG. 12(b), a partition cover 105 may be made of pressed parts such as a copper plate, so that the partition cover 105 is interposed between the conical face 101a of the joint body 101 and the conical face 102a of the nut 102, both of which are formed to sandwich the pipe 103 therebetween. Then, the nut 102 is tightened securely to sandwich the partition cover 105 between the conical faces 101a and 102a, thereby ensuring air tightness at a contact face 105a between the conical face 101a and the partition cover 105. The opening of the pipe joint is thus sealed.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-74768